1. Field of the Invention
The present invention relates to magnetic disk recording systems, and more particularly to apparatus and a method for positioning the read/write head in relation to the disk.
2. The Prior Art
Technical development in magnetic disk storage apparatus is continuing toward increasingly higher storage capacities, with respect to track density, and bit density, which are both characteristics for the storage capacity of the disk surface, as well as with respect to the mechanical structure, in order to accommodate as many as possible magnetic disks in a prescribed mounting space. As an example, the so-called 51/2 inch fixed disk (or hard disk) storage employs a standard mounting space having an overall height of 82.5 mm and a base area of 146 mm.times.203 mm. A fixed disk storage has a fixed (i.e. not replaceable) spindle and disk pack.
In addition to efforts to accommodate as many magnetic disks as possible within this prescribed mounting space, which concern the mechanical structure of the disk pack and its arrangement in the housing of the storage device, there are also attempts to improve the magnetic head positioning mechanism in order to improve access time, positioning precision, and reading reliability. A significant step in the direction toward higher storage density is achieved by use of a positioning method wherein magnetic heads are no longer absolutely positioned relative to the magnetic disks but are positioned relative to a servo track recorded on the disk.
In this positioning method, the positioning mechanism is an integral part of the servo control circuit. Accordingly, the mechanical properties of the positioner mechanism are a factor in determining access time, access precision, the stability of the positioning control loop, and the operational reliability of the disk storage device.
Two different types of positioner mechanisms have been developed, which are referred to as a linear positioner, and a rotational positioner. Linear positioners comprise a positioning carriage carrying the magnetic head positioning arms, this carriage being moved radially relative to the disk pack for the selection of tracks thereon, by means, for example, of a moving coil system. Rotational positioners employ a pivot part which is rotatable about an axis parallel to the axis of the disk pack. This pivot part comprises a one or more positioning arms, each carrying magnetic heads, and also a pair of brackets which lie on opposite sides of the pivoting arms relative to the positioning shaft. The brackets carry either a coil which is subjected to a force as a result of the field of a stationary magnet, or on the other hand carry a magnet, in which case the driving coil is mounted in fixed position. In the former case, the rotational positioner is referred to as a swinging coil positioner, and the later condition is referred to as a magnetic armature positioner.
Both types of rotational positioners are equivalent, in comparison with the above mentioned linear positioner. Rotational positioners are quite frequently employed with smaller magnetic disk storage units, since the mass which has to be moved by them is lower, and they can readily be constructed in small sizes and use little energy. These rotational positioners are therefore faster and lower in inertia, i.e. they are easier to control. Also, they generate less injurious heat inside the disk storage device due to their low energy consumptions.
Such rotational positioners are described for example in IEEE Transactions on Magnetics, Vol. Mag-17, No. 4, July 1981, pages 1392 and following, in Electronics, Apr. 21, 1982, pages 181 and following, and in Mini-Micro Systems, February 1983, pages 143 and following. Given today's storage density, the extremely precise positioning of the magnetic heads on the surfaces of the magnetic storage disks allocated to them is essential. In ongoing operation, the heads fly contact-free above the surface, gliding on an air pillow. When a minimum relative speed between the head and disk is not maintained, this air pillow collapses and the head lands on the disk surface. Such a landing must at all costs not occur in the disk region exploited for the information storage (referred to as the data region). A landing region is therefore defined, and the rotational positioner moves the head to the landing region when it is in idle condition. It must be assured that the rotational positioner is pivotable into the data region only when the disk storage drive is running. An enable magnet is employed for this purpose in known rotational positioners, which functions so as not to release the rotational positioner until after the disk storage drive has been energized. The enable magnet remains actuated during the entire operating time of the disk drive, and thus has to be designed for continuous operation. This contributes to power consumption and the generation of heat. It also contributes a quantity of electromagnetic noise, which may interfere with the normal operation of the disk storage system.